Members of Russia's opposition are to gather in protest over the jailing of one of their leaders, in a test of whether the government will tolerate further dissent or resort to a violent crackdown.

More than 2,000 people have expressed their intent on Facebook to attend the gathering on Thursday in support of Sergei Udaltsov on Pushkin Square, in Moscow. Authorities refused permission for the protest on Wednesday, so the organisers have said it will be held as a public meeting with the opposition MP, Ilya Ponomaryov, which the law technically allows.

Udaltsov, 34, the leader of the radical Left Front group, was sentenced to 10 days in jail on 25 December for allegedly resisting arrest in October. He has spent more than three months behind bars on numerous administrative charges in the last year, in what his lawyers say is a politically motivated campaign of persecution.

The latest sentence caused an outcry that spread this week to even pro-Kremlin bloggers and television personalities. Video footage of a court bailiff refusing to let journalists and an MP enter the supposedly open court hearing provoked further anger.

Street protests in Russia are often broken up by riot police and the authorities frequently deny permission to hold them. A mass opposition rally on 24 December which attracted about 80,000 people was allowed to go ahead in northern Moscow, as was a demonstration of roughly 40,000 people two weeks earlier.

Both rallies – the biggest since the fall of the Soviet Union – called for a rerun of parliamentary elections earlier this month which were widely criticised for alleged fraud in favour of the pro-Kremlin United Russia party.

Public anger has focused on Vladimir Putin, the prime minister, who heads the party. Putin ruled out a rerun of the elections without a court decision this week, but attempted to project a conciliatory tone, suggesting he could meet for negotiations with the opposition. However, he also remarked that the protest movement was not united, saying: "Is there a common platform? No. Who is there to talk to?"

On Tuesday, Vladislav Surkov, the Kremlin "puppet master" who curated internal politics, was transferred from a senior post in the presidential administration to deputy prime minister, in what most analysts saw as a demotion and another sop to the opposition.

President Dmitry Medvedev has also offered a pack of electoral reforms that would make it easier for political parties to register, but which could take months to come into effect.

The protest leaders, including the 35-year-old lawyer Alexei Navalny, remain suspicious of overtures from the ruling elite, including an offer from Alexei Kudrin, a liberal former finance minister who is close to Putin, to act as an intermediary.

Navalny said this week that the opposition would attempt to get 2 million people onto the streets in the run up to the presidential election in March, which Putin is expected to win. "We have to understand that the people who are sitting in the Kremlin and the [Russian government] White House are usurpers, people who are there illegally," Navalny said in a radio interview. "They should be scared."